Process for preparing stable sodium percarbonate

ABSTRACT

Sodium percarbonate is stabilized by a metal chelating agent which will produce a chelate compound insoluble or slightly soluble in water. Such metal chelating agent is dispersed in the reaction mixture with the aid of a surface active agent when sodium carbonate and hydrogen peroxide are reached and the crystals of sodium percarbonate are separated out.

BACKGROUND OF THE INVENTION

1. FIELD OF THE INVENTION

This invention relates to a method of producing sodium percarbonate inthe form of crystals or powder having a long shelf life or an excellentstorage stability.

2. DESCRIPTION OF THE PRIOR ART

It is already known that inorganic peroxides which release active oxygenin an aqueous solution are used as a domestic or industrial bleachingagent or bleaching detergent composition. Among such inorganicperoxides, sodium perborate has a good stability during storage whetherit is used as a bleaching agent or as an additive in a detergentcomposition as it does not substantially decompose during storage tolose available oxygen which is effective for the purpose of bleaching.However, it does not demonstrate its high bleaching effect unless it isused at a temperature over 60° C., so that this substance cannot show asufficient bleaching effect in a country where laundering is generallyperformed at a low temperature.

On the other hand, sodium percarbonate has a higher solubility in waterthan sodium perborate and is also easily dissolved in cold water. Sodiumpercarbonate has the formula: 2Na₂ CO₃.3H₂ O₂. It is generally preparedby reacting 2 mols of sodium carbonate with 3 mols of hydrogen peroxide.However, if sodium percarbonate is mixed in a powdery detergentcomposition or bleaching agent composition, it is decomposed too rapidlyunder the atmospheric conditions where the temperature exceeds 30° C.and the humidity is higher than 80% RH, so that no satisfactorybleaching effect can be obtained in a high-temperature high-humidityatmosphere. Various attempts have been made for improving the stabilityduring storage of sodium percarbonate, and there have been proposed thefollowing processes for stabilizing sodium percarbonate:

(1) A method in which an inorganic salt known as a peroxide stabilizer,such as, for example, sodium silicate, magnesium silicate, magnesiumoxide, sodium chloride or sodium sulfate, is added to sodiumpercarbonate.

(2) A method in which an organic metal chelating agent of thewater-soluble polyaminocarboxylic acid type, such as, for example,ethylenediaminetetraacetate, nitrilotriacetate ordiethylenetriaminepentaacetate, is added to sodium percarbonate.

(3) A method in which sodium percarbonate is granulated or coated with awater-soluble or water-insoluble or slightly water-soluble compound suchas paraffin wax, polyethyleneglycol or alkanolamide.

These known methods, however, were not satisfactory, because they areinsufficient with respect to their stabilizing effect on sodiumpercarbonate and a considerable decomposition of sodium percarbonate iscaused during storage, or they are too complicated for practical use, orthe water-solubility of sodium percarbonate is reduced remarkably in theprocess of coating the same.

SUMMARY OF THE INVENTION

The present invention has for its object to provide a method ofproducing sodium percarbonate having a better stability during storagethan those obtained from the conventional stabilizing methods such asabove-mentioned. The sodium percarbonate product obtained by the processof the present invention is stable both when it is stored by itself andwhen it is stored in the form of a mixture with detergents ordecomposition promoting agents.

The object of the present invention is attained by a process forpreparing stable sodium percarbonate by mixing sodium carbonate or anaqueous solution thereof and a hydrogen peroxide solution, characterizedin that the crystals of sodium percarbonate are precipitated out in thepresence of a chelating agent which will produce a water-insoluble orslightly water-soluble chelate compound with a heavy metal and a surfaceactive agent. Such heavy metal will catalyze the decomposition of sodiumpercarbonate.

The chelating agents to be used in the method of the present inventioninclude the following: oxine, salicylaldoxime, α-benzoinoxime, cupferon,aluminon, anthranilic acid, α-nitroso-β-naphthol, β-nitroso-α-naphthol,2-methyloxine, 5-methyloxine, 6-methyloxine, 7-methyloxine,8-hydroxy-2-phenylquinone, 1-hydroxyacyzine, 7-allyl-8-quinolinol,7-allyl-5-nitroso-8-quinolinol, 5,7-dichlorooxine, 5,7-dibromooxine,quinaldic acid, quilinone-8-carboxylic acid, benzoylphenylhydroxylamine,salicylic acid, β-resorcinolic acid, P-aminosalicylic acid,5-nitrosalicylic acid, 3-bromosalicyclic acid, 5-bromo-1-resorcinolicacid, 1-hydroxy-2-naphthoic acid, 1-hydroxy-4-bromo-2-naphthoic acid,1-nitroso-2-hydroxy-3-naphthoic acid and 2-hydroxy-1-naphthoaldehyde.

Generally, metal chelating agents are classified into the following twotypes: the chelating agents which will form water-soluble chelatecompounds with metal ions and those which will form water-insoluble orslightly water-soluble chelate compounds with metal ions to separate outprecipitates in water. The former type of chelating agents are usuallycalled inhibitors or sequestering agents, and they includepolyaminocarboxylic acids such as nitrilotriacetate andethylenediaminetetraacetate. These inhibitors have been conventionallyused as decomposition retarders for the peroxides, and theabove-mentioned prior art method (2) utilizes this property. However,these agents are not satisfactory in their effect of retardingdecomposition of sodium percarbonate, and particularly when sodiumpercarbonate is mixed in a detergent composition, their decompositionretarding effect is further lowered.

On the other hand, the latter type of chelating agents, which are usedin the method of the present invention, are considered because they maybe able to show an excellent decomposition retarding effect, which couldnever be obtained from the conventional methods, by having suchchelating agents coexist with the starting materials in the productionof sodium percarbonate. However, such chelating agents are mostlyinsoluble or slightly soluble in water, so that it was extremelydifficult to have them coexist uniformly in the aqueous solution ofsodium carbonate or hydrogen peroxide solution in the preparation ofsodium percarbonate. Thus, these chelating agents, if added alone,cannot exhibit a satisfactory decomposition prevention effect.

According to the present invention, a surface active agent is added todisperse such water-insoluble or slightly soluble chelating agent inwater so that such chelating agent will coexist uniformly in the aqueoussodium carbonate solution or hydrogen peroxide solution. Such surfaceactive agent is also adsorbed or deposited on the produced sodiumpercarbonate to increase the efficiency of the chelating agent toimprove its stabilizing effect.

The surface active agents to be used in the present invention may beanionic or nonionic surface active agents. Examples of the anionicsurface active agents to be used in the present invention are: higherfatty acid salts, higher alcohol sulfates, alkylsulfonates,alkyldisulfonates, sulfonated oils and sulfonated fatty acid salts,sulfates of polyoxyethylenealkylethers, sulfates of alkylolamides ofhigher fatty acids, salts of sulfoalkyl compounds of higher fatty acids,alkylbenzenesulfonates, alkylphenolsulfonates,alkylnaphthalenesulfonates, and alkyldiphenylsulfonates. In the abovecompounds, the carbon numbers of alkyls, higher fatty acids and higherfatty alcohols are 8-18 and the cations are usually sodium or ammonium.

The nonionic surface active agents to be used in the present inventioninclude the following: ethylene oxide addition products of higher fattyacids, ethylene oxide addition products of higher alcohols, ethyleneoxide addition products of higher alkylamines, ethylene oxide additionproducts of higher fatty acid amines, ethylene oxide addition productsof higher alkylmercaptanes, ethylene oxide addition products ofalkylphenols, glycerinesters of higher fatty acids, glycolesters ofhigher fatty acids, pentaerythritolesters of higher fatty acids,sorbitanesters of higher fatty acids, or ethylene oxide additionproducts of sorbitanesters of higher fatty acids. Also, in thesecompounds, the carbon number of alkyls, higher fatty acids and higheralcohols are 8-18.

In the method of the present invention, the chelating agent and thesurface active agent may be added either in an aqueous solution ofsodium carbonate or in a hydrogen peroxide solution, and also the orderof mixing may be selected suitably. Thus, it is possible to obtainsimilar stable sodium percarbonate either by adding a sodium carbonatesolution containing a chelating agent and a surface active agent, to ahydrogen peroxide solution or by adding a hydrogen peroxide solution tosaid sodium carbonate solution, or by adding a hydrogen peroxidesolution containing a chelating agent and a surface active agent to anaqueous solution of sodium carbonate, or by adding a sodium carbonatesolution to said hydrogen peroxide solution. Also, solid sodiumcarbonate may be added to a hydrogen peroxide solution containing achelating agent and a surface active agent.

In case an anionic surface active agent is used, the sodium percarbonateproduced according to the method of the present invention does not formlumps or cakes when the produced sodium percarbonate is separated fromthe mother liquor and is dried, and even if it may form lumps, suchlumps are extremely brittle and can be easily crushed into powders.Also, even if it is stored for a long time, it will be substantiallyfree of caking and will maintain an excellent fluidity.

In the process for preparing sodium percarbonate according to the methodof the present invention, the chelating agent is added generally in anamount of 0.001 to 10 weight%, preferably 0.005 to 1.0 wt.% based on thetotal amount of the aqueous solutions containing sodium carbonate and anequivalent amount of hydrogen peroxide. On the other hand, the surfaceactive agent may be used in any suitable amount if it provides asufficient concentration to make the chelating agent soluble ordispersable in the aqueous solution, but a too high concentration isundesirable in view of its solubility in water. Therefore, it is usuallyused in a concentration of less than 5 weight%, preferably in an amountof 0.001 to 0.5 wt.% based on the total amount of the aqueous solutionscontaining sodium carbonate and an equivalent amount of hydrogenperoxide.

Now the present invention is described in further detail by way of somepreferred embodiments thereof in order to clarify the excellent effectsof the invention.

EXAMPLE 1 Preparation of sodium percarbonate

0.1 Gram of oxine and 1 gr of sodium dodecylbenzenesulfonate weredissolved in 5 ml of ethanol, and the mixture was poured into 500 ml ofwater and well agitated. Then 210 gr of sodium carbonate was added anddissolved in the mixture, followed by the further addition of 340 gr of30% aqueous hydrogen peroxide solution to react with the mixture. Thesolution was then cooled to 0° to 5° C. and the produced crystals ofsodium percarbonate were filtered out. These crystals were then driedeither under a reduced pressure of 20 mmHg at about 30° C. or naturallyin air to obtain powdery sodium percarbonate. There were also preparedsodium percarbonate powder products in the same way as described aboveexcept there were used various other kinds of chelating agents andsurface active agents as shown in Table 1.

Storage stability test

The thus prepared samples of sodium percarbonate were left in anatmosphere of 40° C. temperature and 80% relative humidity for 20 days,and then the remaining available oxygen concentration of each sample wasmeasured. The ratio of the remaining available oxygen concentration tothe initial available oxygen concentration was expressed by percentageas remaining activity. For the sake of comparison, the remainingactivity was determined with respect to the sodium percarbonate productwhich was prepared in the same way without adding any chelating agentand with respect to the sodium percarbonate product prepared similarlywithout using any surface active agent. The results are shown in Table1.

                  Table 1                                                         ______________________________________                                                               Remaining                                                                     activity (%)                                           ______________________________________                                                          Con-          Con-       No                                                   cen-          cen- Chel- chel-                              Sam- Surface      tra-          tra- ating ating                              ple  active       tion   Chelating                                                                            tion agent agent                              No.  agent        (%)    agent  (%)  added added                              ______________________________________                                        1      None       0      Oxine  0.01 32    10                                 2    Sodium dodecyl-                                                                            0.1    "      0.01 78    14                                      benzenesulfonate                                                         3    "            0.2    "      0.2  85    13                                 4    Sodium dodecyl-                                                                            0.1    "      0.01 80    15                                      sulfate                                                                  5    Sodium oleate                                                                              0.2    "      0.2  65    12                                 6    Polyoxyethylene-                                                                           0.05   "      0.01 60    18                                      dodecylether                                                             7    "            0.05   α-nit-                                                                         0.1  56    18                                                          roso-                                                                         β-naph-                                                                  thol                                                 8    Polyethylene-                                                                              0.05   Oxine  0.01 52    20                                      glycol-                                                                       monolaurate                                                              9    Sodium dodecyl-                                                                            0.1    α-ben-                                                                         0.1  40    14                                      benzenesulfonate    zoin-                                                                         oxime                                                10   "            0.1    Salicy-                                                                              0.05 75    14                                                          lald-                                                                         oxime                                                11   Sodium dodecyl-                                                                            0.1    Cupferon                                                                             0.1  42    13                                      sulfate                                                                  12   "            0.1    α-ben-                                                                         0.1  48    13                                                          zoin-                                                                         oxime                                                ______________________________________                                    

As is apparent from the results shown in the above Table 1, sodiumpercarbonate prepared by adding a chelating agent which produces awater-insoluble or slightly water-soluble chelate compound and a surfaceactive agent according to the method of the present invention has abetter storage stability than those prepared without adding suchchelating agent and/or surface active agent.

EXAMPLE 2

Sodium percarbonate prepared by adding a chelating agent and a surfaceactive agent according to the process of Example 1 was blended in adetergent (A) having the following composition at a ratio of 15 parts byweight of sodium percarbonate to 85 parts by weight of the detergentcomposition (A) to prepare a powdery bleaching detergent, and this wasleft standing in an atmosphere of 40° C. temperature and 80% relativehumidity for 6 days, and then the remaining available oxygenconcentration of sodium percarbonate was measured by a conventionalmethod.

Composition of detergent (A):

    ______________________________________                                                            weight%                                                   ______________________________________                                        Sodium alkylbenzenesulfonate                                                                        20.0                                                    Sodium tripolyphosphate                                                                             20.0                                                    Sodium silicate       5.0                                                     Sodium carbonate      1.0                                                     Carboxymethylcellulose                                                                              1.0                                                     Fluorescent dye, perfume                                                                            0.7                                                     Sodium sulfate        42.3                                                    Water                 10.0                                                    ______________________________________                                    

The results are shown in Table 2. The remaining activity of sodiumpercarbonate is expressed by the ratio of the available oxygenconcentration measured immediately after blending to the remainingavailable oxygen concentration after 6 days, expressed as a percentage.

                  Table 2                                                         ______________________________________                                                               Remaining                                                                     activity %                                             ______________________________________                                                          Con-          Con-       No                                                   cen-          cen-  Chel-                                                                              chel-                              Sam- Surface      tra-          tra-  ating                                                                              ating                              ple  active       tion   Chelating                                                                            tion  agent                                                                              agent                              No.  agent        (%)    agent  (%)   added                                                                              added                              ______________________________________                                        1      None       0      Oxine  0.01 15    2                                  2    Sodium dodecyl-                                                                            0.1    "      0.1  82    1                                       benzenesulfonate                                                         3    "            0.2    "      0.2  85    1                                  4    Sodium dodecyl-                                                                            0.1    "      0.01 79    2                                       sulfate                                                                  5    Sodium oleate                                                                              0.2    "      0.2  75    2                                  6    Polyoxyethylene-                                                                           0.05   "      0.01 33    5                                       dodecylether                                                             7    "            0.05   α-nit-                                                                         0.1  28    5                                                           roso-                                                62 -naph-                                                                                              thol                                                 8    Polyethylene-                                                                              0.05   Oxine  0.01 24    4                                       glycol-                                                                       monolaurate                                                              9    Sodium dodecyl-                                                                            0.1    α-ben-                                                                         0.1  28    1                                       benzenesulfonate    zoin-                                                                         oxime                                                10   "            0.1    Salicyl-                                                                             0.05 77    1                                                           aldoxime                                             11   Sodium dodecyl-                                                                            0.1    Cupferon                                                                             0.1  52    2                                       sulfate                                                                  12   "            0.1    α-ben-                                                                         0.1  36    2                                                           zoin-                                                                         oxime                                                ______________________________________                                    

It is known from the above-shown results that the bleaching detergentcompositions, incorporated with the sodium percarbonate product preparedfrom a system containing a chelating agent which will produce awater-insoluble or slightly water-soluble chelate compound and a surfaceactive agent, have a storage stability better than that of the detergentcompositions containing no chelating agent, and that, even when the samechelating agent is used, sodium percarbonate prepared according to themethod of the present invention shows a better storage stability thanthat added with no surface active agent and is well comparable in itsstorage stability to sodium perborate which is a stable bleaching agent.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:
 1. In a process forpreparing stable sodium percarbonate which comprises mixing sodiumcarbonate or an aqueous solution thereof, with an aqueous solution ofhydrogen peroxide, to effect a reaction therebetween to form sodiumpercarbonate and recovering the produced crystals of sodium percarbonatefrom the reaction mixture, the improvement which comprises; one of saidaqueous solutions contains dissolved or dispersed therein, prior to saidmixing, from 0.001 to 10 weight percent of a chelating agent selectedfrom the group consisting of oxine, salicylaldoxime, α-benzoinoxime,cupferon, aluminon, anthranilic acid, α-nitroso-β-naphthol,β-nitroso-α-naphthol, 2-methyloxine, 5-methyloxine, 6-methyloxine,7-methyloxine, 8-hydroxy-2-phenylquinone, 1-hydroxyacyzine,7-allyl-8-quinolinol, 7-allyl-5-nitroso-8-quinolinol, 5,7-dichlorooxine,5,7-dibromooxine, quinaldic acid, quilinone-8-carboxylic acid,benzoylphenylhydroxylamine, salicylic acid, β -resorcinolic acid,p-aminosalicyclic acid, 5-nitrosalicylic acid, 3-bromosalicylic acid,5-bromo-1-resorcinolic acid, 1-hydroxy-2-naphthoic acid,1-hydroxy-4-bromo-2-naphthoic acid, 1-nitroso-2-hydroxy-3-naphthoic acidand 2-hydroxy-1-naphthoaldehyde, and from 0.001 to 0.5 weight percent ofan anionic surface active agent selected from the group consisting ofhigher fatty acid salts, higher alcohol sulfates, alkylsulfonates,alkyldisulfonates, sulfonated oils and sulfonated fatty acid salts,sulfates of polyoxyethylenealkylethers, sulfates of alkylolamides ofhigher fatty acids, salts of sulfoalkyl compounds of higher fatty acids,alkylbenzenesulfonates, alkylphenolsulfonates,alkylnaphthalenesulfonates, and alkyldiphenylsulfonates wherein thenumber of carbon atoms in the alkyl, fatty acid and fatty alcoholmoieties are from 8 to 18, or a nonionic surface active agent selectedfrom the group consisting of ethylene oxide addition products of higherfatty acids, ethylene oxide addition products of higher alcohols,ethylene oxide addition products of higher alkylamines, ethylene oxideaddition products of higher fatty acid amines, ethylene oxide additionproducts of higher alkylmercaptans, ethylene oxide addition products ofalkylphenols, glycerin esters of higher fatty acids, glycol esters ofhigher fatty acids, pentaerythritol esters of higher fatty acids,sorbitan esters of higher fatty acids, and ethylene oxide additionproducts of sorbitan esters of higher fatty acids wherein the number ofcarbon atoms in the alkyl, fatty acid and alcohol moieties are from 8 to18, wherein both percentage ranges are based on the total weight of anaqueous solution containing said sodium carbonate and an equivalentamount of hydrogen peroxide.
 2. A process as claimed in claim 1, whereinsaid chelating agent is added in an amount of 0.005 to 1.0% by weightbased on the total amount of the aqueous solutions containing sodiumcarbonate and an equivalent amount of hydrogen peroxide.
 3. A process asclaimed in claim 1 in which said chelating agent is oxine.
 4. A processas claimed in claim 1 in which said chelating agent isα-nitroso-β-naphthol.
 5. A process as claimed in claim 1 in which saidchelating agent is α-benzoinoxime.
 6. A process as claimed in claim 1 inwhich said chelating agent is salicylaldoxime.
 7. A process as claimedin claim 1 in which said chelating agent is cupferon.
 8. A process asclaimed in claim 3 in which said anionic surface active agent is sodiumdodecylbenzene sulfonate.
 9. A process as claimed in claim 3 in whichsaid anionic surface active agent is sodium dodecyl sulfate.